Addition agent and its use



Patented Nov. 19, 1940 James H. Critchett, Douglaston, and WalterCrafts, Niagara Falls, N. Y., assignors to Electro MetallurgicalCompany, a corporation of West Virginia No Drawing. Original applicationApril 14,1938, Serial No, 201,931. Divided and this application December1, 1938, Serial No. 243,324.

May 9,1940

Renewed 8 Claims. (01. 75-58) Theinvention relates to the treatment ofmolten iron and steel to promote a fine grain structure and freedom fromdeleterious impurities. This application is a division of ourapplication Serial No. 201,931, filed April 14, 1938.

During manufacture, steels become contaminated with certain oxides andoccluded gases, which, if not substantially removed or renderedinnocuous, detrimentally affect the soundness and physical properties ofthe finished steel. To overcome the deleterious eflects of suchimpurities, an addition of ferrosilicon or ferromanganese, or both, asdeoxidizers, is usually made to the steel shortly before casting intoingots orv other shapes. For further deoxidation, and to provide aninherently fine-grained steel having inhibited, grain growth tendenciesat elevated temperatures, a later addition of aluminum is often made tothe molten steel.

Aluminum additions,"in the amounts, for the purposes, and in the mannerdescribed above, tend to produce a steel containing deleterious typesand qualities of non-metallic inclusions. It has been proposed tosubstitute for the aluminum other agents, such as vanadium, or titanium,but none of these elements is entirely satisfactory. Vanadium is usuallytoo expensive to add in an amount suflicient to produce the desired.

. results, and titanium asyheretofore used tends to produce a steelcontaining numerous objectionable non-metallic impurities.

According to.the present invention, a steel that is substantially freefrom deleterious, gaseous or solid non-metallic impurities and that hasimproved mechanical properties (including improved impact strength) andexcellent fine grain characteristics is produced-by adding to the steelwhile it is molten in the ladle or otherwise shortly before casting, anaddition agent containing 25% to 85% (preferably 35% to of silicon,remainder iron and at least two elements selected from the following twogroups: (1) beryllium, magnesium, calcium, barium, strontium, boron, andaluminum; (2) vanadium, columbium,

and tantalum, at least one element being present from each group, eachin an amount at least 3%. Iron is present as an impurity or diluentunavoidably introduced in producing an economical and commerciallypracticable material, and should'not exceed about 65%.

- described is preferably atleast 10% but not over of the composition ofthe addition agent. If the number of elements in said mixture is onlytwo.

The total amount of the elements selected from the groups herein agent,and if such number is more than two, said total amount preferablyexceeds 25% by not more than 5% for each of said elements above Apreferred addition agent composition exceed 25% of the-composition ofthe addition contains 45% to silicon, 5% to l5%'aluminum, and 5% to 15%columbium, the remainder...

iron.

The constituents of the addition agent are preferably prealloyed in'theform of a master alloy; but they may be unalloyed or onlypartiallyalloyed, and used in the form of a briquet of comminutedmaterial. Also, some of the constituents thereof may suitably be in theform of easily reducible or decomposable compounds such as nitrides,nitrates or mixtures thereof. It is essential, however, that theconstituents be closely associated, because successive additions do notyield the tion.

In general, the more complex the addition improved results of the inven-V agent, that is, the greater the number of deoxiof the addition agentmay be varied. If lessgrain refinement is required, part of the siliconrequired for deoxidizing may be added as' the agent of the invention andpart as ordinary'ferrosilicon, and if more grain-refinement is-required,the action of the addition agent may be supplemented by an addition ofaluminum or other grain refiner.

The desired compositio n may be added to the steel in any well knownmanner, for example, in the furnace, in the ladle, or in the molten ofthe several constituents separately to the steel stream during pouring.When adding the addition agent to the steel either in the ladle or in ithe molten stream, an agent containing less than No. 6 or Nu. '7 mayreadily be procured in steels treated according to a method of theinvention. Throughout the present specification, grain size refers toaustenitic or inherent grain size determined by the McQuaid-Ehncarburizing test conducted at a temperature of 925 C. for 8 hours, asdefined by the A. S. T. M. specification E 1933. The degree of grainrefinement or deoxidation of the steel per unit of addition agent addedwill vary, not only with the combination of elements selected, but alsowith the type of steel being treated, so that the total amount of agentto be added to the steel for best results must be determined by trial.Ordinarily, this total amount of agent will be less than 5%, and mostfrequently less than 1%.

While the addition agents of this invention are especially useful in thetreatment of steels which are to be hot worked, the invention is alsoapplicable to the treatment of steels which are to be employed ascastings. Used for the latter purpose, it has been found that, in manyinstances, the characteristics of the casting may be improved if thematerial of the invention is added in an amount which is sufficient todeoxidize the metal, yet is insuflicient to develop harmful inclusions.

Steels treated according to the invention are sound, substantially freefrom excessive non-metallic inclusions, and possess improved ductilityand shock resistance. Further, the few inclusions distributed throughoutsuch steels are more uniform than diverse, that is, the majority of theinclusions which usually accompany any deoxidizing treatment'thatproduces small grain size are not noticeable in the steels deoxidized inaccordance with the invention until a higher degree of grain refinementis attained than that attainable by the addition of aluminum alone.

We claim:

1. A method of treating molten ferrous metal which comprises adding tothe molten ferrous metal a grain refining amount less than 1% of anaddition agent consisting of 25% to 85% sili con, iron, and at least oneelement selected from each of the following groups: (1) beryllium,magnesium, calcium, barium, strontium, boron, and aluminum; (2)vanadium, columbium, and tantalum; the total percentage of elements fromeach group being between 3% and 20%.

2. A method of treating molten ferrous metal which comprises adding tothe molten ferrous metal a grain refining amount less than 1% of anaddition agent consisting of 25% to silicon, iron, and at least oneelement selected from each of the following groups: (1) beryllium,magnesium, calcium, barium, strontium, boron, and aluminum; (2)vanadium, columbium, and tantalum; the total percentage of elements fromeach group being between 3% and 20%, and the sum of the elements of bothof said groups being at least 10% and not exceeding 25% by more than 5%for each of said elements above two.

3. A method of treating molten ferrous metal which comprises adding tothe molten ferrous metal a grain refining amount less than 1% of anaddition agent containing 35% to 55% silicon; 3% to 20% of at least oneelement selected from the group beryllium, magnesium, calcium, barium,strontium, boron, and aluminum; 3% to 20% of at least one elementselected from the group vanadium, columbium, and tantalum;rand theremainder iron.

4. A method of deoxidizing molten iron or steel which comprises addingto the molten iron or steel a grain refining amount less than 1% of anaddition agent containing 35% to 55% silicon, 3% to 20% aluminum, 3% to20% columbium; and the remainder iron.

5. A composition of matter, suitable for use as an addition agent fortreating molten ferrous metal, consisting substantially of 25% tosilicon, iron, and at least one element selected from each of thefollowing groups: (1) beryllium, magnesium, calcium, barium, strontium,boron, and aluminum; (2) vanadium, columbium, and tantalum; the totalpercentage of elements from each group being between 3% and 6. Acomposition of matter for use as an addition agent for treating moltenferrous metal, containing 25% to 65% silicon, iron, and at least oneelement selected from each of the following groups: (1) beryllium,magnesium, calcium, barium, strontium, boron, and aluminum; (2)vanadium, columbium, and tantalum; the total percentage of elements fromeach group being in an amount between 3% and 20%, and the sum of theelements of both of said groups being at least 10% and not exceeding 25%by more than 5% for each of said elements above two.

'7. A composition of matter for use as an addition agent for treatingmolten ferrous metal, containing 35% to 55% silicon; 3% -to 20% of atleast one element selected from the group beryllium, magnesium, calcium,barium, strontium, boron, and aluminum; 3% to 20% of at least oneelement selected from the group vanadium, columbium, and tantalum; andthe remainder iron.

8. An addition agent for deoxidizing molten iron or steel, containing35% to 55% silicon; 3% to 20% aluminum, 3% to 20% columbium; theremainder iron.

' JAMES H. CRITCHETT.

WALTER CRAFIS.

